Ophthalmologists often use images of the retinal fundus (i.e., the interior lining of the eyeball, including the retina, the optic disc, and the macula) to diagnose and monitor the development of eye diseases. For example, retinal fundus imaging is one of the leading image technologies used for the diagnosis of diabetic retinopathy, age-related macular degeneration (DR), hypertensive retinopathy, and systemic diseases (e.g., stroke), among other conditions. The developments and applications of computer-aided diagnosis (CAD) systems for detecting different types of diseases in retinal imaging have been increasing rapidly in recent years.